Charge dissipative floor tiles

ABSTRACT

A surface covering product having static dissipative electrical properties comprises a consolidated agglomeration of individual chips of polymeric material and wherein at least a portion of said individual chips contain an antistatic agent. A second portion of individual chips contain no antistatic agent or a reduced amount of antistatic agent.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.078,899 filed July 29, 1987, now U.S. Pat. No. 4,826,912, issued May 2,1989, in the names of Kenneth K. Ko, et al. and entitled "ChargeDissipative Floor Tiles".

FIELD OF THE INVENTION

The present invention relates to surface covering products. Inparticular, the present invention relates to surface covering productshaving static dissipative electrical properties.

BACKGROUND OF THE INVENTION

Static control problems have been recognized and routinely addressed foryears in the electronic manufacturing industries. As the miniaturizationof electrical equipment progresses and the growth of the electronicindustry continues, static control problems have become more and more asubject of serious concern to the electronics industry. To put theproblem into perspective, it is known that someone walking across acarpeted floor can accumulate more than 30,000 volts of static charge.While published literature has referred to 25 to 100 volts as criticalstatic discharges which could cause immediate and catastrophic damage toa sensitive electronic chip. This demonstrates the need for protectingthe areas and environments where sophisticated electronics equipment aremanufactured and stored.

It has been generally recognized that the prevention of static dischargerequires that the total manufacturing and storage environment beconstructed of materials which are capable of dissipating staticcharges, and that these materials be connected to a common ground. Insuch an environment, it is critically important that the flooringstructure be protected against electrostatic discharge.

It has long been known that polymeric materials, of the kinds typicallyemployed in flooring structures, such as polyvinyl chloride, arenormally insulative. They can be made conductive, however, byincorporating either a conductive filler or an antistatic agent in thepolymer structure or by employing both methods at the same time. Whenconductive fillers, such as metallic materials or carbon blacks, areused, the filler concentrations required to impart conductivity to thepolymer structure are usually relatively high, typically thirty to fiftypercent by Volume. At such concentrations, the appearance of thepolymeric structure is usually black, gray, or brown, depending upon thematerials employed, and are not suitable for highly decorative floortile applications.

To protect a floor structure from accumulating dirt and to improve thelustre or glossiness of a floor structure, a floor polish is often usedas a maintenance aid. For most commercial conductive floor tiles orsheet materials, especially those made with carbon and other metallicmaterials, i.e., commercially available carbon veined tiles and thelike, such maintenance aids are not recommended by the manufacturers.This is because most commercially available floor polish materials areinsulative. They will interfere with the conducting path formed by thecarbon particles, or other metallic materials therein, affecting theability of the conductive flooring structure to dissipate staticcharges.

For similar reasons, even a conductive floor polish is often notrecommended for use in the maintenance of conductive floors, such asthose employing carbon-veined tiles. This is typical because theconductive floor polish is not usually as conductive as the conductivefloor itself. In addition, the residual polish worn away by traffic alsointerferes with the conducting path, further decreasing the chargedissipative efficiency of the conductive floor structure.

Antistatic agents, such as those containing quaternary ammonium saltfunctionalities have been known to impart charge dissipative propertiesto flooring structures in the past. However, these antistatic materialsare sensitive to moisture and, in previous uses, have effected themanufacturing processing characteristics and performance characteristicsof the flooring structures in which they were employed. For example, afloor structure containing moisture absorptive materials might swell orgrow in length where water is present. If the moisture growth is high,the floor structure might curl or buckle, causing what is commonlyreferred to as a peak-seam in an installed floor structure. Highmoisture growth is, therefore, generally considered to be a high riskwith respect to the performance of floor coverings, particularly wheninstalled on on-grade or below-grade concrete sub-floors.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a surface coveringproduct having static dissipative electrical properties suitable forhighly decorative floor tile applications.

It is a further object of the present invention to provide a surfacecovering product having static dissipative electrical properties whichcan be maintained with commonly available commercial floor careproducts.

It is a still further object of the present invention to provide asurface covering product having static dissipative electrical propertieswithout the moisture growth problems typical of antistatic agents.

According to the present invention, there is provided a surface coveringproduct having static dissipative electrical properties, which surfacecovering product comprises a consolidated agglomeration of individualchips of polymeric material and wherein at least a portion of saidindividual chips contain an antistatic agent. In one preferredembodiment, a first portion of the individual chips contains asubstantial amount of an antistatic agent and a second portion containssubstantially less antistatic agent.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

By far, the predominant form of resilient flooring used today is of thevinyl type. That is, flooring which has a binder system based onpolyvinyl chloride, commonly referred to as PVC. This polymer by itselfis a very hard, tough, virtually intractable, thermoplastic materialthat must be compounded with various additives to produce economicallyuseful products. It is one of the most adaptable polymeric materials andis used for applications as widely divergent as rigid pipe to almostjelly-like fishing lures. Because of this adaptability it is well suitedto the manufacture of both flexible and semi-rigid flooring materials.

Polyvinyl chloride's high molecular weight and chemical and physicalnature allow it to accommodate relatively large amounts of inert fillerand it can be plasticized effectively and permanently to creatematerials with a wide range of flexibilities. Polyvinyl chloride isinherently resistant to acids, alkali and many organic solvents. It doesnot hydrolyse even when in continuous contact with moisture. Because ofits chlorine content, the polymer is also inherently fire resistant andas a plastic material is generally classified as self-extinguishing.Plasticized material is less fire resistant than rigid PVC, but canusually be formulated for use as a floor covering to pass the flamespread and smoke generation limitations of most building codes.

When properly compounded and processed, PVC can be a clear, colorlessmaterial or pigmented to produce the full range of colors in transparentor opaque forms.

Polymeric material, as used throughout this specification, is intendedto include polyvinyl chloride in its various forms. The vinyl resinsused in flooring may be homopolymers, i.e., polymers consisting of onlyvinyl chloride units, or copolymers, consisting of vinyl chloride andother structural units, such as vinyl acetate. The molecular weights ofthese resins typically range from about 40,000 to about 200,000 atomicmass units. The higher molecular weight polymers have greater ultimatetensile strength and abrasion resistance and are generally used inflooring wear layers, while the lower molecular weight polymers are mostuseful in producing foams for cushioned flooring. As a general rule,vinyl homopolymers are typically used in vinyl sheet goods and Type IIIsolid vinyl tile, while Type IV vinyl composition tiles typicallycontain copolymers of vinyl chloride and vinyl acetate.

To protect the polymeric material from degredation during processing andduring its use as flooring material, vinyl compounds must be stabilizedagainst the effects of heat and ultraviolet radiation. The most commonstabilizers used in flooring are soaps of barium, calcium and zinc;organo-tin compounds; epoxidized soy bean oils and tallate esters; andorganic phosphites.

Polymeric materials for flooring uses, even for use in relatively rigidType IV vinyl composition tiles, contain plasticizers to provideflexibility and to facilitate processing. The most frequently usedplasticizer is dioctyl phthalate (DOP). Others that may be found inflooring use include butylbenzyl phthalate (BBP), alkylaryl phosphates,other phthalate esters of both aliphatic and aromatic alochols,chlorinated hydrocarbons, and various other high boiling esters. Theselection of the proper type and amount of plasticizer is often criticalin the formulation of flooring compounds because of the interaction offlexibility requirements, resistance to staining, reaction withmaintenance finishes, and processing requirements.

In most tile and sheet flooring, the stabilized and plasticized vinylformulation is mixed with varying amounts of inorganic filler to providemass and thickness at a reasonable cost. The most common fillertypically found in flooring is crushed limestone (calcium carbonate).Others that may be employed include talcs, clays and feldspars. Inaddition to providing bulk at reasonable cost, the use of inorganicfillers in flooring structures provides increased dimensional stability,resistance to cigarette burns, improved flame spread ratings and reducedsmoke generation.

Pigments are used in flooring products to provide both opacity and colorto the finished products. The typically preferred white pigment istitanium dioxide and colored pigments are preferably inorganic. Certaincolors only available as lakes, such as the phthalocyanine blues andgreens, must be resistant to the effects of alkali and light fading.

Finally, in order to pass certain code requirements with regard to fireand smoke properties various additives may be employed to reduce flamespread and smoke generation ratings. These compounds include aluminatrihydrate, antimony trioxide, phosphate or chlorinated hydrocarbonplasticizers, zinc oxide, and boron compounds. Cushioned flooringcontaining chemically expanded foam is usually compounded withazobisformamide blowing agents. Various other processing aids andlubricants may also be employed.

Probably the most widely used resilient flooring product is vinylcomposition tile, as described by Federal Specification SS-T-312b, TypeIV, Composition I. While the present invention is intended for use insuch tile, as the specification and Examples describe, it will beobvious to one skilled in the art that the principles will also beapplicable to various other types of flooring, particularly sheetflooring formed from stencil lay-ups or fused particles.

A typical formulation for vinyl composition tile is:

    ______________________________________                                                      Percent by Weight                                               ______________________________________                                        Vinyl Resin     12.5                                                          Hydrocarbon Resin                                                                             2.5                                                           Plasticizer     4.0                                                           Stabilizer      1.0                                                           Fillers and Pigments                                                                          80.0                                                          ______________________________________                                    

Vinyl composition tile is highly filled and the primary filler iscalcium carbonate, or crushed limestone. The ingredients are typicallymixed in a high power, high shear, heated mixer, such as a BanburyMixer, to combine and fuse them together into a heavy dough-like mass.This mass is then banded on a two roll mill and in the manufacture ofgrained or jaspe'd tile, accent colors, of the same or a similarcomposition material, may be added to the mill nip.

For the purposes of the present invention, however, the material can besheeted and cooled, then cut into individual chips of regular orirregular dimension. An assortment of such chips prepared in suitablecolors are then arranged in a metal frame and consolidated with heat andpressure into an aggomeration.

Alternatively, non-conductive chips and conductive chips, separatelyprepared, may be mechanically mixed, such as in a Baker Perkin mixer,and subsequently sheeted out as a mixed-chip conductive structure usinga two-roll mill.

A factory finish may be applied to the hot consolidated aggomeration toenhance colors, provide uniform gloss, prevent blocking in storage andprotect the product during installation. Such finishes, as well as waxfinishes applied to conductive flooring in use have in the past acted toinsulate flooring material unless such finishes and waxes wereformulated to be conductive. For reasons which are as yet unexplained,such conductive finishes and waxes do not appear to be necessary withthe products of the present invention as the products of the presentinvention appear to maintain their conductive properties even with theapplication of a limited amount of conventional finishes and waxes.

Vinyl composition tile is typically offered in several gauges and sizesdepending on intended end use. For residential applications, vinylcomposition tile is offered in so-called service gauge which is 1/16inch thick.

For commercial markets, vinyl composition tile is typically offered in3/32 inch and 1/8 inch gauges, the latter being most frequentlyspecified for heavy traffic. The standard size of vinyl composition tileis 12 inches by 12 inches, although other sizes may be commerciallyavailable.

The performance requirements, outlined in Federal SpecificationSS-T-312b, include size, thickness, squareness, and dimensionalstability tolerances. These factors are critically important in thefinished appearance of the installed tile floor. Other characteristicscontained in the specification are solvent resistance, indentationrequirements, deflection, volatility, and impact resistance.

Vinyl composition tile is a fairly rigid material, and at roomtemperature will not bend acutely without breaking. However, ifdeflected very slowly, it will bend. This attribute is necessary tosuccessfully install the material over normal subfloors that are notperfectly flat allowing it to conform to subfloor irregularities.Commercial installation of vinyl composition tile is usually done with afull spread of asphalt adhesive and the tile is set into the adhesiveafter the solvent has evaporated. Solventless adhesives are alsoavailable containing emulsified asphalt and resins for areas wheresolvent vapors are undesirable. Rubber latex adhesives also are usedwhere black asphalt adhesives would be undesirable and for use overpreexisting tile floors. Such adhesives are often available inconductive forms for us with the tile of the present invention.

Vinyl composition tile is generally considered the standard or basegrade commercial finish flooring. It has the lowest relative installedcost and has per formed satisfactorily in commercial environments formany years. The major market segment for such tile use today is themercantile market, where vinyl composition tile has been used almostexclusively for the general floor area of grocery stores, supermarkets,and discount department stores. It is also used extensively in schools,health care facilities and to a lesser extent in offices, banks, andlight industries.

There is no minimum binder level requirement for Type IV (vinylcomposition) tile, and this is the primary difference between vinylcomposition tile and Type III vinyl tile or "solid" vinyl tile. TheFederal Specification SS-T-312b requires that the minimum binder levelof Type 111 tile shall not be less than 34%, and defines binder toinclude vinyl resin(s), plasticizers and stabilizers. Vinyl tile isconsiderably more flexible than vinyl composition tile, but it is alsosignificantly more expensive, because of its higher binder level.

Until the present invention, static dissipative flooring of the vinylcomposition tile type has not been commercially successful, chieflybecause of moisture growth problems. Type III vinyl tile alternativescontaining conductive material, however, have remained expensivealternatives.

There are two general classes of materials available which willdissipate static charges. The first class of these is referred to as"conductive" materials, and typically have resistivities in the range of10₃ to 10⁶ ohms/square. Charge dissipative materials, or staticdissipative materials, the second class, typically have resistivities inthe range of 10⁶ to 10¹¹ ohms/square.

Static dissipative electrical properties as referred to herein, meansthat the resistivity of a material should be less than 10¹¹ ohms/square.In addition, a material should have a charge decay rate, for 5000 voltsto 0 volts, of no more than 2.0 seconds.

Type III vinyl flooring tiles are commercially available whichincorporate carbon black or metallic materials. These tiles, because ofthe coloration of the high filler content, are not believed to besuitable for highly decorative floor tile applications. In addition,because of the cost of the conductive filler material, and the highbinder level, such tiles tend to be expensive.

Vinyl composition flooring tiles have previously been known which haveemployed antistatic agents containing quaternary ammonium saltfunctionalties. However, these were flooring tiles of the kind known as"straight grain", in which the antistatic agent was substantiallyuniformly distributed. Such products, while they met the staticdissipative electrical property requirements, defined above,demonstrated serious moisture growth problems which may have limitedtheir usefulness in certain applications.

It has now been determined that a slightly modified construction offlooring tile, employing a compressed aggomeration of individual chips,can achieve the same or similar electrical properties without themoisture growth problems known to the prior art.

This has been accomplished, quite surprisingly, by limiting the presenceof the antistatic agent to only a portion of the individual chips orminimizing the amount of the antistatic agent in a portion of theindividual chips. As the examples which follow will demonstrate, staticdissipative electrical properties are affected only slightly, whilemoisture growth properties fall dramatically as the proportion ofindividual chips containing a charge dissipating amount of antistat isreduced. While even a small reduction in the proportion of chipscontaining the typical level of antistat will serve the purposes of thepresent invention, it has been demonstrated that better results areobtained if the proportion of chips containing a charge dissipatingamount of antistat represent between from about twenty-five (25%) toabout eighty-five (85%) by weight of the overall composition. Stillbetter results are obtained if the proportion of chips containing thecharge dissipating amount of antistat represent between from aboutthirty-five percent (35%) and about seventy percent (70%) by weight ofthe overall composition.

Although it is assumed that other antistatic agents may be operable inthe practice of the present invention, such agents containing quaternaryammonium salt functionalties have demonstrated static dissipativeelectrical properties in flooring tiles which meet other physicalrequirements. Such antistatic agents include Larostat 264A. commerciallyavailable from the Jordan Chemical company; Cyastat LS, commerciallyavailable from American Cyanamid; and Hexcel 106G, commerciallyavailable from the Hexcel Corporation.

As detailed in the Examples which follow, it has been found,surprisingly, that the charge dissipative tiles of the present inventionmay be maintained with minimal applications of commonly availablecommercial floor care products without significant loss of their chargedissipative characteristics. In fact, some data generated seems toindicate that an increase in such characteristics may be measured.Applicants do not propose any explanation for the increased conductivityof the normally insulative floor finishing material.

EXAMPLE 1

Vinyl composition tiles were prepared by mixing and consolidating vinylcomposition material in chip form. Specifically, the vinyl compositionmaterial had the following formulation in parts by weight:

    ______________________________________                                        Polyvinyl chloride resin                                                                           121.00                                                   Hydrocarbon resin    10.00                                                    Phthalic ester plasticizer                                                                         40.50                                                    Stabilizer           6.00                                                     Titanium dioxide (opacifier)                                                                       7.80                                                     Crushed Limestone (40 mesh)                                                                        815.00                                                   ______________________________________                                    

To a portion of this material was added 1.5% of an antistatic agent,Larostat 264A, commercially available from the Jordan Chemical Company.After dicing both vinyl structures into chips with a dimension of about1/4 inches, floor tiles were prepared by mixing the chips in theproportions shown in Table 1 and filling a metal frame. The chips weresubsequently hotpressed for ten (10) minutes at 310° F., at a pressureof 1000 pounds per square inch. Electrical properties and moisturegrowth characteristics for the resulting tiles are also given in Table1.

                                      TABLE 1                                     __________________________________________________________________________              Surface Resistivity Surface Resistivity                                       at 50% Relative Humidity                                                                          at 15% Relative Humidity                        Ratio of Chips      Tile Mounted on     Tile Mounted On                                                                         Charge Decay                Containing Anti-    a Plywood Board     a Plywood Board                                                                         Rate at 13%                 stat to Chips Not   With a Conductive   With a Conductive                                                                       Relative                                                                              Moisture            Containing Antistat                                                                     Tile Alone                                                                              Adhesive  Tile Alone                                                                              Adhesive  Humidity                                                                              Growth              __________________________________________________________________________    100/0     1.8 × 10.sup.8 ohm/sq                                                             8.7 × 10.sup.7 ohm/sq                                                             8.7 × 10.sup.9 ohm/sq                                                             3.7 × 10.sup.8                                                                    0.01 sec.                                                                             5.61%               60/40     2.0 × 10.sup.8 ohm/sq                                                             8.5 × 10.sup.7 ohm/sq                                                             1.9 × 10.sup.9 ohm/sq                                                             4.5 × 10.sup.8                                                                    0.02 sec.                                                                             1.25%               50/50     4.0 × 10.sup.8 ohm/sq                                                             1.0 × 10.sup.8 ohm/sq                                                             8.9 × 10.sup.8 ohm/sq                                                             6.5 × 10.sup.8                                                                    0.02 sec.                                                                             0.84%               45/55     5.3 × 10.sup.8 ohm/sq                                                             4.2 × 10.sup.8 ohm/sq                                                             3.4 ×  10.sup.9 ohm/sq                                                            1.7 × 10.sup.9                                                                    0.04 sec.                                                                             0.66%               40/60     5.7 × 10.sup.8 ohm/sq                                                             3.2 × 10.sup.8 ohm/sq                                                             3.0 × 10.sup.9 ohm/sq                                                             6.5 × 10.sup.8                                                                    0.03 sec.                                                                             0.32%               35/65     1.6 × 10.sup.9 ohm/sq                                                             5.4 × 10.sup.8 ohm/sq                                                             1.5 × 10.sup.10 ohm/sq                                                            2.4 × 10.sup.9                                                                    0.48 sec.                                                                             0.16%               0/100     5.0 × 10.sup.13 ohm/sq                                                            1.5 × 10.sup.13 ohm/sq                                                            6.0 × 10.sup.13 ohm/sq                                                            3.0 × 10.sup.13                                                                    >6 sec.                                                                              0.14%               __________________________________________________________________________

EXAMPLE 2

Vinyl composition tiles were prepared from the conductive andnon-conductive chips prepared in Example 1. Such chips were combined inthe proportions set out in Table II, mechanically mixed in a BakerPerkin mixer, and subsequently sheeted out using a two-roll mill and cutinto tiles. As shown in Table II, the vinyl composition tiles preparedin this manner possessed electrical dissipative properties andmechanical properties similar to the tiles of Example 1.

                                      TABLE 2                                     __________________________________________________________________________              Surface Resistivity Surface Resistivity                                       at 50% Relative Humidity                                                                          at 15% Relative Humidity                        Ratio of Chips      Tile Mounted on     Tile Mounted On                                                                         Charge Decay                Containing Anti-    a Plywood Board     a Plywood Board                                                                         Rate at 13%                 stat to Chips Not   With a Conductive   With a Conductive                                                                       Relative                                                                              Moisture            Containing Antistat                                                                     Tile Alone                                                                              Adhesive  Tile Alone                                                                              Adhesive  Humidity                                                                              Growth              __________________________________________________________________________    0/100     >10.sup.13                                                                         ohm/sq                                                                             >10.sup.13                                                                         ohm/sq                                                                             >10.sup.13                                                                          ohm/sq                                                                            >10.sup.13                                                                         ohm/sq                                                                              >10 sec.                                                                             0.43%               50/50 cubes                                                                             2.0 × 10.sup.8                                                               ohm/sq                                                                             8.5 × 10.sup.7                                                               ohm/sq                                                                             1.9 × 10.sup.9                                                                ohm/sq                                                                            4.5 × 10.sup.8                                                               ohm/sq                                                                             0.12 sec.                                                                             2.4%                40/60 cubes                                                                             4.0 × 10.sup.8                                                               ohm/sq                                                                             1.0 × 10.sup.8                                                               ohm/sq                                                                             8.9 × 10.sup.8                                                                ohm/sq                                                                            6.5 × 10.sup.8                                                               ohm/sq                                                                             0.28 sec.                                                                             2.0%                35/65 cubes                                                                             5.3 × 10.sup.8                                                               ohm/sq                                                                             4.2 × 10.sup.8                                                               ohm/sq                                                                             3.4 × 10.sup.9                                                                ohm/sq                                                                            1.7 × 10.sup.9                                                               ohm/sq                                                                             0.61 sec.                                                                             1.85%               50/50 chips                                                                             5.7 × 10.sup.8                                                               ohm/sq                                                                             3.2 × 10.sup.8                                                               ohm/sq                                                                             3.0 × 10.sup.9                                                                ohm/sq                                                                            6.5 × 10.sup.8                                                               ohm/sq                                                                             0.05 sec.                                                                             1.5%                40/60 chips                                                                             1.6 × 10.sup.9                                                               ohm/sq                                                                             5.4 × 10.sup.8                                                               ohm/sq                                                                             1.5 × 10.sup.10                                                               ohm/sq                                                                            2.4 × 10.sup.9                                                               ohm/sq                                                                             0.08 sec.                                                                             1.2%                __________________________________________________________________________

EXAMPLE 3

A volume of vinyl composition tiles were prepared by separately mixingbatches of materials having the compositions listed by weights in Table3A in a Baker-Perkin mixer. Each batch had a temperature of between 280°F. to 2856° F. at the end of about fifteen (5) minutes of mixing. Mottlechips or accent colors prepared of the same compositions beforehand wereadded and mixing continued for approximately one minute at the sametemperature.

Each mixed vinyl composition was then sheeted off in a mill to make ajaspe blanket. The front mill roll was adjusted to approximately 210° F.while the back roll was maintained between 250° F. and 270° F. Theblanket was then die-cut into cubes or furnish.

After batches A through F were converted into cubes in this manner, theywere blended and mixed in an equal ratio and transferred to a metalscreen carrier. The mixed vinyl cubes were then carried through achamber heated to between 330° F. and 350° F., to partially soften thevinyl cubes. The mixed and temperature conditioned cubes were then fedthrough a set of calender rolls equipped with an oscillating blade toconsolidate the structure. The temperature of the top roll wasmaintained between 220° F. and 225° F., while the bottom roll wasmaintained at between 330° F. and 350° F.

After this consolidation step, the blanket was reheated and fed into aconsolidator to effect the final guage reduction and facing operationbefore being punched into twelve inch by twelve inch (12"×12")one-eighth inch (1/8) thick tiles.

The tile produced in this manner met the indentation, impact resistance,deflection and volatility requirements of Federal SpecificationSS-T-312B for Type IV vinyl composition tile. Dimensional properties didnot meet specification requirements, but it was believed that processingadjustments would overcome this problem. The tiles also demonstratedexcellent electrical charge dissipating characteristIcs, as shown inTable 3B.

                  TABLE 3A                                                        ______________________________________                                                  Product Formulations (%)                                                      A    B       C      D     E    F                                    ______________________________________                                        Limestone   80.35  81.05   80.75                                                                              78.60 79.25                                                                              78.93                              Pigments    2.00   1.30    1.60 1.95  1.30 1.62                               Antistat    0.00   0.00    0.00 1.60  1.60 1.60                               (Larostat 264-A)                                                              Vinyl Resin 11.45  11.45   11.45                                                                              12.65 12.65                                                                              12.65                              Hydrocarbon 1.15   1.15    1.15 1.15  1.15 1.15                               Resin                                                                         Plasticizer 4.40   4.40    4.40 3.40  3.40 3.40                               Stabilizer  0.65   0.65    0.65 0.65  0.65 0.65                               ______________________________________                                    

                  TABLE 3B                                                        ______________________________________                                        Surface Resistivity                                                           Relative Humidity                                                                          Tile Alone Tile with Conductive                                  (%)          (ohms/sq.) Adhesive (ohms/sq.)                                   ______________________________________                                        50           6 to 9 × 10.sup.8                                                                  2 to 4 × 10.sup.8                               15           4 to 7 × 10.sup.9                                                                  5 to 8 × 10.sup.8                               ______________________________________                                        NFPA 99 Resistance                                                            2 to 10 × 10.sup.6 ohms                                                 (measured with Meggameter)                                                    ______________________________________                                        Static Decay Rate                                                             (5000 Volts to 0 Volts at 15% Relative Humidity                               Tile Alone          0.06 to 0.08 seconds                                      Tile with Conductive                                                                              0.01 to 0.02 seconds                                      Adhesive                                                                      ______________________________________                                        Triboelectric Charging                                                        Measured at 50% Relative Humidity with a                                      NASA Rubbing Wheel Tribocharge Test Apparatus)                                2000 to 4000 Volts                                                            ______________________________________                                    

EXAMPLE 4

This example compares the use of commercial conductive floor polish inmaintaining commercially available carbon-veined conductive floor tileand the charge dissipative tile of this invention as prepared in Example3. In this example, nine (9) 12"×12"tiles selected from each ofcommercial carbon-veined tiles, charge dissipative tiles of Example 3and commercially-available vinyl composition tiles were installed in acontiguous side by side array in a hallway over a cement substrate floorbase. A commercially-available carbon filled latex-base conductiveadhesive, measured to have a surface resistivity of 4×10⁵ ohms/square,was used for the installation. After cleaning the tiles with detergentand clean water to clear dirt from the tile surface, four coats of acommercially-available conductive floor polish were applied to the tilesfollowing ordinary and typical floor polish application procedures. Thesurface resistivities of the coated floor tiles were monitoredperiodically after the conductive floor wax was applied and the resultsof these measurements are reported in Table 4. The resistivitymeasurements were done in accordance with the ASTM D-257 method using aconcentric ring electrode, the Ike Probe from the Electro-tech SystemInc., and a Dr. Thiedig Milli-TO multi range resistivity meter forregistering the read out. As shown in the table, the initialconductivity, which is the inverse of the resistivity, of the coatedcarbon-veined conductive tile is about the same in magnitude as thenon-conductive vinyl composition tile. For the charge dissipative tiles,however, the conductive floor polish shows a synergistic effect inconductivity yielding a conductivity higher than that of the untreatedcharge dissipative tiles or the vinyl tile with conductive floor wax. Itshould be noted further that the conductivity of the treated chargedissipative tiles was measured to be higher than the conductivitymeasured for either treated or non-treated carbon-veined tiles.

After one week with traffic, the conductive floor wax appeared topartially wear off, as indicated by the loss in conductivity of thetreated vinyl tiles, but the treated charge dissipative tiles stillshowed higher conductivity then the non-treated charge dissipative tilesamples. The treated carbon-veined tiles, on the other hand, shows amuch greater loss in conductivity. In this case, the conductivity of theconductive polish treated carbon-veined tiles was measured to be aboutone order of magnitude lower than the conductivity of non-treatedcarbon-veined tiles.

After two weeks of traffic and Wear, the conductive polish appeared towear off further, and the conductivity of the treated vinyl tile wasfurther reduced. While the conductivity of the treated carbon-veinedtiles were still lower than the conductivity of the untreatedcarbon-veined tiles, no loss in conductivities were measured in thenon-treated and treated charge dissipative tiles of the presentinvention.

EXAMPLE 5

This example demonstrates the effects of using a non-conductive floorpolish in the maintenance of charge dissipative floor tiles. The chargedissipative tile samples installed on a cement base substrate describedin Example 4 were stripped and cleaned following ordinary floormaintenance procedures. One coat of a floor finish coating (a commercialacrylic base floor polish material) was applied to a portion of thecharge dissipative tile samples. The surface resistivities of treatedand non-treated charge dissipative tiles were monitored in a similarfashion as described in Example 4. No loss in conductivity was foundbetween the treated and non-treated charge dissipative tile samples asshown in Table 5. The treated charge dissipative tiles, however,demonstrated superior resistance to dirt pickup when compared to thenon-treated charge dissipative tiles.

EXAMPLE 6

When a floor polish is used in maintaining conductive floor tiles in anESD protected area, it requires that the polish should not interferewith the charge dissipating efficiency of the tile and that thetriboelectric charge generation should be no greater than the generationof the tile alone. In this example, the triboelectric charging ofuntreated charge dissipative tile and charge dissipative tile coatedwith a commercial acrylic floor polish were compared. The measurement oftriboelectric charging was done in accordance with the AATCC Test Method134-1979 (Electrostatic propensity of Carpets, AATCC Test Method134-1979, American Association of Textile Chemist and Colorists,Research Triangle Park, N.C., revised 1979), commonly known as the "steptest". Four different types of shoe sole materials were used in thistest, they include neoprene A, neoprene B, leather and neolite. Table 6summarizes the charge generation measured at different humidities. Asshown, the triboelectric charges generated from the untreated chargedissipative tile and the charge dissipative tile treated with one coatof a commercial acrylic floor polish are about the same.

                                      TABLE 4                                     __________________________________________________________________________                  One Day After Treatment                                                                    Seven Days After Treatment                                                                  Fourteen Days After Treatment                      (ohms per square at                                                                        (ohms per square at                                                                         (ohms per square at                                55% Relative Humidity)                                                                     45% Relative Humidity)                                                                      52% Relative Humidity)               __________________________________________________________________________    Charge Dissipative Tile                                                                     4.5 × 10.sup.7                                                                       8.5 × 10.sup.7                                                                        4.0 × 10.sup.7                 Charge Dissipative Tile                                                                     7.5 × 10.sup.6                                                                       3.0 × 10.sup.7                                                                        1.5 × 10.sup.7                 with Conductive Polish                                                        Commercial Carbon-Veined                                                                    3.6 × 10.sup.7                                                                       3.0 × 10.sup.7                                                                        1.5 × 10.sup.7                 Conductive Tile                                                               Commercial Carbon-Veined                                                                    4.2 × 10.sup.7                                                                       5.0 × 10.sup.8                                                                        5.5 × 10.sup.8                 Conductive Tile with                                                          Conductive Polish                                                             Commerical PVC Tile                                                                         >10.sup.15   >10.sup.15    >10.sup.15                           Commercial PVC Tile                                                                         4.2 × 10.sup.7                                                                       2.10 × 10.sup.9                                                                       .sup. 1.9 × 10.sup.10          with Conductive Polish                                                        __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________                One Day After Treatment                                                                    Seven Days After Treatment                                                                  Fourteen Days After Treatment                      (ohms per square at                                                                        (ohms per square at                                                                         (ohms per square at                                55% Relative Humidity)                                                                     45% Relative Humidity)                                                                      52% Relative Humidity)                 __________________________________________________________________________    Charge Dissipative Tile                                                                   4.5 × 10.sup.7                                                                       8.5 × 10.sup.7                                                                        4.0 × 10.sup.7                   Charge Dissipative Tile                                                                   4.2 × 10.sup.7                                                                       9.0 × 10.sup.7                                                                        4.6 × 10.sup.7                   with Commerical Non-                                                          Conductive Polish                                                             __________________________________________________________________________

                  TABLE 6                                                         ______________________________________                                                    Neo-   Neo-                                                                   prene A                                                                              prene B  Leather  Neolite                                  ______________________________________                                                    Triboelectric Charge                                                          (Volts at 33% Relative Humidity)                                  Commercial PVC Tile                                                                         2010     870      3100   5050                                   Commercial PVC Tile                                                                          600     340       980   2030                                   with Commercial Non-                                                          Conductive Polish                                                             Charge Dissipative Tile                                                                      30      141       64     298                                   Charge Dissipative Tile                                                                      32      -100      50    -194                                   with Commercial Non-                                                          Conductive Polish                                                                         Triboelectric Charge                                                          (Volts at 50% Relative Humidity)                                  Commercial PVC Tile                                                                          460     --        949   2060                                   Charge Dissipative Tile                                                                       3      -24        6     -7                                    Charge Dissipative Tile                                                                     -10      -36      -15    -72                                    with Commercial Non-                                                          Conductive Polish                                                             ______________________________________                                    

EXAMPLE 7

To avoid waste, improve consolidation and improve processing in themanufacture of floor tiles, it is standard practice to recycle the punchframe scrap into the vinyl composition tile batch in the form of aremix. Of course, since the punch frame scrap includes some antistaticagent, this recycling of the remix introduces a low level of antistaticagent throughout any composition in which the remix is added.

In this example, the remix was added to both of the fresh or virgincompositions, the first including antistatic agent and the secondincluding no antistatic agent. Note that since the mottle which containsno antistatic agent is added at the end of the mixing step to break upthe base batch of mixed virgin and remix compositions to improve feedingof the tile composition through the mill chute, the mottle compositionis not intimately mixed and the tile compositions includes mottle areaswhich do not contain an antistatic agent.

The tile sample was made by preparing chips 50% of which containedantistatic agent and 50% of which did not contain antistatic agent. Theformulations are set forth below in parts by weight.

    ______________________________________                                                          With        Without                                                           Antistat    Antistat                                        ______________________________________                                        Base Material                                                                 Virgin Formulation                                                            Polyvinyl chloride resin                                                                          336.0         303.0                                       Alpha methyl styrene tackifier                                                                    24.0          24.0                                        Phthalic ester plasticizer                                                                        49.4          99.0                                        Stabilizer          14.4          14.4                                        Titanium dioxide opacifier                                                                        130.7         98.8                                        Crushed limestone   1790.2        1860.8                                      Antistat-Larostat 264A                                                                            55.3          --                                                              2400.0        2400.0                                      Remix               600.0         600.0                                       Mottle              780.0         780.0                                                           3780.0        3780.0                                      ______________________________________                                    

Two mottles were prepared at a thickness of 100 mils with two differentpigmentations. The formulation in parts by weight for the mottles were:

    ______________________________________                                        Polyvinyl chloride resin                                                                           83.6                                                     Alpha methyl styrene tackifier                                                                     14.2                                                     Phthalic ester plasticizer                                                                         30.2                                                     Stabilizer            6.6                                                     Titanium dioxide opacifier                                                                         22.4                                                     Crushed limestone    623.0                                                                         780.0                                                    ______________________________________                                    

Each mottle has premixed in an Eirich mixer for about three minutes,brought to a temperature of about 340° F. to about 370° F. in a Farrelmixer in about 30 seconds, and sheeted off a two roll mill to athickness of about 100 mils. The sheet was ground into chips having aminimum dimension of about 1/4 inch to about 3/4 inch.

The virgin formulation was charged into a Type F mixer with remix. Theremix was formed by grinding punch frame scrap and reject tiles intoabout 1/4 inch chips. The virgin formulation and remix were mixed in thepresence of heat in a Type F mixer for about 17 minutes. The mottle wasthen added and the mixing continued for about two minutes. Theantistatic and nonantistatic vinyl composition of mottle and basematerial were sheeted off a mill and diced into chips. The chips werethen blended in a 50/50 ratio and reconsolidated under heat and pressurein a tile line calendar to make the finished static dissipative tile.

The moisture growth of the finished tile was 0.6% with acceptableelectrical properties. See Table 7 following Example 8 At equilibriumthe percent antistatic agent is as follows:

    ______________________________________                                                     With           Without                                                        Antistat       Antistat                                          ______________________________________                                        Virgin         2.3%             0%                                            Remix          0.87%            0.87%                                         Base           2.02%            0.17%                                         Mottle         0%               0%                                            ______________________________________                                    

Since the mottle is not homogeneously distributed within the tile chips,there are regions (approximately 20%) of the chip without anY antistaticagent. About 40% of the chip has 2.0% antistatic agent and about 40% ofthe chip has 0.17% antistatic agent.

EXAMPLE 8

To simplify the manufacturing process and reduce the chance of errors,the above described process was modified to introduce the antistaticagent only in the mottle. Since the base material of intimately mixedvirgin and remix formulations include antistatic agent from the remix,some antistatic agent is distributed throughout the tile composition.However, the concentration of antistatic agent in the base material isnot high enough to contribute substantially to the moisture growthproblem or have the desired static dissipative properties. Such a levelof antistatic agent is deemed to be an insubstantial amount. Preferablythe amount of antistatic agent in the base material is less than 0.25%and less than one tenth of the antistatic composition in the mottle.

The antistatic mottle composition was prepared by premixing thefollowing formulation (in parts by weight) in an Eirich mixer for aboutsix minutes.

    ______________________________________                                        Antistatic Mottle                                                             ______________________________________                                        Polyvinyl chloride resin                                                                           242.0                                                    Alpha methyl styrene tackifier                                                                     20.0                                                     Phthalic ester plasticizer                                                                         48.0                                                     Stabilizer           17.2                                                     Titanium dioxide opacifier                                                                         21.4                                                     Crushed limestone    1612.4                                                   Larostat 264A antistatic agent                                                                     39.0                                                                          2000.0                                                   ______________________________________                                    

The mottle composition was then brought up to about 340° F. to 370° F.in a Farrel mixer in about 30 seconds. The mixed composition was thensheeted off a two roll mill to a thickness of about 100 mils and groundinto chips.

It is surprising and unexpected that the antistatic agent containingmottle can be fused in a Farrel mixer. One would expect the antistaticagent to be destroyed at the temperatures reached in the high intensityFarrel mixer. However, the antistatic agent is subjected to the highintensity mixing for only a brief time.

The fresh or virgin composition had the following formulation in partsby weight:

    ______________________________________                                        Virgin Composition                                                            ______________________________________                                        Polyvinyl chloride resin                                                                           70.0                                                     Alpha methyl styrene tackifier                                                                     5.6                                                      Phthalic ester plasticizer                                                                         23.5                                                     Stabilizer           3.4                                                      Titanium dioxide opacifier                                                                         6.0                                                      Crushed limestone    451.5                                                                         560.0                                                    ______________________________________                                    

The virgin composition and remix were processed in a manner similar toExample 7. Two tests were run, the first with 40% mottle and the secondwith 33.3% mottle. The following pounds of the components were chargedinto Type F mixers. The percent of the tile composition is indicated inthe parenthesis.

    ______________________________________                                                   Test 1      Test 2                                                 ______________________________________                                        Remix        160 (11.9%)   240 (20%)                                          Virgin       640 (47.4%)   560 (46.7%)                                        ______________________________________                                    

After mixing for about 17 minutes 550 lbs. (40.7%) mottle was added inTest I and 400 (33.3%) mottle was added in Test 2. After addition of themottle, mixing was continued for about two minutes. The tile compositionwas then sheeted, diced into about 1/4 inch cubes, and reconsolidatedunder heat and pressure using an oscillating blade in a calendar nip.

If the mottle and base material are different colors or shades, astraight grain or, mottled or jaspe sheet is produced. By blending cubesof different colors before the reconsolidation, a wide variety ofpattern coloration and design can be achieved.

The surface resistivity of tiles made by the processes of Examples 7 and8 were as follows:

                  TABLE 7                                                         ______________________________________                                        Surface Resistivity                                                           Relative            Example 8  Example 8                                      Humidity                                                                              Example 7   (40% mottle)                                                                             (33.3% mottle)                                 (%)     (ohms/sq)   (ohms/sq)  (ohms/sq)                                      ______________________________________                                        50      1.6 × 10.sup.9                                                                      1.6 × 10.sup.9                                                                     1.3 × 10.sup.9                           15      .sup. 8.5 × 10.sup.10                                                               .sup. 4.9 × 10.sup.10                                                              .sup. 5.6 × 10.sup.10                    ______________________________________                                    

What is claimed is:
 1. A surface covering product having staticdissipative electrical properties comprising a composition of aconsolidated agglomeration of individual chips of polymeric materialwherein a first portion of said individual chips are electricallyconductive and a second portion of said individual chips areelectrically non-conductive.
 2. A surface covering product having staticdissipative electrical properties comprising a composition of aconsolidated agglomeration of individual chips of polymeric materialwherein a first portion of said individual chips contain a substantialamount of an antistatic agent and a second portion of said individualchips contain only an insubstantial amount of antistatic agent, thefirst portion representing between about twenty-five percent ( 25%) andabout eight-five percent (85%) by weight of the overall composition. 3.A surface covering product having static dissipative electricalproperties comprising a composition of a consolidated agglomeration ofindividual chips of polymeric material wherein a first portion of saidindividual chips contain a substantial amount of an antistatic agent anda second portion of said individual chips contain only an insubstantialamount of antistatic agent, said first portion containing between aboutone quarter of one percent and about five percent by weight of theantistatic agent.
 4. The surface covering product of claim 3 wherein thefirst portion contains between about one percent and about two percentby weight of the antistatic agent.
 5. A surface covering product havingstatic dissipative electrical properties comprising a composition of aconsolidated agglomeration of individual chips of polymeric materialwherein a first portion of said individual chips contain a substantialamount of an antistatic agent and a second portion of said individualchips contain only an insubstantial amount of antistatic agent, saidantistatic agent having quaternary ammonium salt functionalities.
 6. Thesurface covering product of claim 5, wherein the antistatic agent ismixed in the first portion with a high intensity mixer.
 7. A surfacecovering product having static dissipative electrical propertiescomprising a composition of a consolidated agglomeration of individualchips of polymeric material wherein a first portion of said individualchips contain a substantial amount of an antistatic agent and a secondportion of said individual chips contain only an insubstantial amount ofantistatic agent, said second portion containing less than one quarterof one percent by weight of antistatic agent.
 8. A surface coveringproduct having static dissipative electrical properties comprising acomposition of a consolidated agglomeration of individual chips ofpolymeric material wherein a first portion of said individual chipscontain a substantial amount of an antistatic agent and a second portionof said individual chips contain only an insubstantial amount ofantistatic agent, the percentage of antistatic agent in the secondportion being no more than one tenth the percentage of antistatic agentin the first portion.
 9. A surface covering product having staticdissipative electrical properties comprising a composition of aconsolidated agglomeration of individual chips of polymeric materialwherein a first portion of said individual chips contain a substantialamount of an antistatic agent and a second portion of said individualchips contain only an insubstantial amount of antistatic agent, theantistatic agent in said second portion being the result of introducingscrap material from a previous manufacturing run into the startingmaterial of said second portion, said starting material containingsubstantially no antistatic agent.
 10. A surface covering product havingstatic dissipative electrical properties comprising a composition of aconsolidated agglomeration of individual chips of polymeric materialwherein a first portion of said individual chips contain a substantialamount of an antistatic agent and a second portion of said individualchips contain only an insubstantial amount of antistatic agent, saidantistatic agent in the second portion being substantially uniformlydistributed within each individual chip of the second portion.
 11. Thesurface covering product of claim 1 wherein the individual chips of thefirst and second portions are substantially uniformly distributed withinthe upper exposed layer of the surface covering.
 12. A surface coveringproduct having static dissipative electrical properties comprising acomposition of a consolidated agglomeration of individual chips ofpolymeric material wherein a first portion of said individual chipscontain a substantial amount of an antistatic agent, a second portion ofsaid individual chips contain only an insubstantial amount of antistaticagent and a third portion of individual chips which contain noantistatic agent.
 13. A surface covering product having staticdissipative electrical properties comprising a composition of aconsolidated agglomeration of individual chips of polymeric materialwherein a first portion of said individual chips contain a substantialamount of an antistatic agent and a second portion of said individualchips contain only an insubstantial amount of antistatic agent, saidsecond portion of the individual chips having a resistivity of greaterthan 10¹¹ ohms/sq.